The present invention relates to a semiconductor device and a method of fabricating the same and, more particularly, to a device using radio-frequency signals and a method of fabricating the same.
RF (Radio Frequency) communication devices using RF signals are often fabricated by using an SOI (Silicon On Insulator) wafer which uses, as a support substrate, a high-resistance substrate (resistivity xcfx81xe2x89xa71,000 xcexa9xc2x7cm) formed by crystal pulling by the CZ method, in order to suppress energy loss of an RF signal and form a spiral inductance having a high Q value even in the GHz band. This fabrication method improves the RF characteristics.
Unfortunately, if the interstitial oxygen concentration (to be referred to as [Oi] hereinafter) in the semiconductor substrate is high, heat-treating performed during the device process for forming a circuit in the substrate generates oxygen donors and lowers the resistivity of the substrate. Hence, a substrate having a low [Oi] ([Oi]xe2x89xa68E17 cmxe2x88x923) must be used.
The oxygen concentration can be decreased by
(1) crystal pulling by the MCZ method, or
(2) heat-treating a substrate having a high [Oi] ([Oi]xe2x89xa713E17 cmxe2x88x923) to form bulk micro defect (to be referred to as BMD hereinafter) by oxygen precipitation, thereby reducing the concentration of a solid solution of oxygen.
When an RF device is formed using a substrate obtained by method (1) above, however, slip occurs in heat-treating during the device process because the pinning effect of dislocation by a solid solution of oxygen lowers. This is a phenomenon in which, when heat-treating is performed by supporting a semiconductor substrate by a 4-point-supporting boat, cracks and the like occur in portions where the substrate contacts the boat.
When an RF device is formed using a substrate obtained by method (2) above, it is possible to prevent the occurrence of slip in the boat contact portions during heat-treating by the pinning effect of dislocation by oxygen redissolving from BMD. However, thermal stress during the device process forms slip on the entire surface of the substrate.
As described above, it is conventionally impossible to effectively prevent slip in a high-resistance substrate having a low [Oi]. This lowers the yield by defects caused by slip.
It is, therefore, an object of the present invention to provide a semiconductor device capable of preventing defects caused by slip and improving the yield by using a high-resistance substrate having excellent RF characteristics, and provide a method of fabricating the same.
A semiconductor device of the present invention is a semiconductor device obtained by forming a circuit in a surface portion of a semiconductor substrate, wherein the semiconductor substrate has an interstitial oxygen concentration (to be referred to as [Oi] hereinafter) of 8E17 cmxe2x88x923 or less, an oxygen precipitate density (to be referred to as [BMD] hereinafter) of 1E8 cmxe2x88x923 or more, and a resistivity of 500 xcexa9xc2x7cm or more.
The circuit can be formed in the surface portion of the semiconductor substrate by a device process including a heat-treating step of 25 hrs or less as a value calculated assuming that the temperature is 1,000xc2x0 C.
The semiconductor substrate is obtained by performing heat-treating at 500 to 700xc2x0 C. for 5 hrs or less for a semiconductor substrate having an [Oi] of 8E17 cmxe2x88x923 or less, and a resistivity of 500 xcexa9xc2x7cm or more, thereby setting [BMD] of 1E8 cmxe2x88x923 or more, and the circuit can be formed in the surface portion of the semiconductor substrate by a device process including a heat-treating step of 25 hrs or less as a value calculated that assuming that the temperature is 1,000xc2x0 C.
The semiconductor substrate has a [BMD] of 1E8 cmxe2x88x923 or more, which is obtained by doping 1E13 cmxe2x88x923 or more of [N] during crystal pulling, and also has an [Oi] of 8E17 cmxe2x88x923 or less and a resistivity of 500 xcexa9xc2x7cm or more, and the circuit can be formed in the surface portion of the semiconductor substrate by a device process including a heat-treating step of 25 hrs or less as a value calculated assuming that the temperature is 1,000xc2x0 C.
A method of fabricating a semiconductor device by forming a circuit by using a semiconductor substrate according to the present invention comprises the step of performing a heat-treating step of a device process for forming the circuit for 25 hrs or less as a value calculated assuming that the temperature is 1,000xc2x0 C., by using a semiconductor substrate having an [Oi] of 8E17 cmxe2x88x923 or less, a [BMD] of 1E8 cmxe2x88x923 or more, and a resistivity of 500 xcexa9xc2x7cm or more.
The method can further comprise the step of obtaining the semiconductor substrate by performing heat-treating at 500 to 700xc2x0 C. for 5 hrs or less for a semiconductor substrate having an [Oi] of 8E17 cmxe2x88x923 or less, and a resistivity of 500 xcexa9xc2x7cm or more, thereby setting a [BMD] of 1E8 cmxe2x88x923 or more.
The method can further comprise the step of obtaining the semiconductor substrate having a [BMD] of 1E8 cmxe2x88x923 or more, which is obtained by doping 1E13 cmxe2x88x923 or more of [N] during crystal pulling, and also having an [Oi] of 8E17 cmxe2x88x923 or less and a resistivity of 500 xcexa9xc2x7cm or more.